Some of the money vehicles powering 2016 presidential race

WASHINGTON (AP) — Under election rules, campaigns can only raise $2,700 per donor, per election, but outside groups supporting presidential candidacies face no such limits.

To overcome restrictions against directly working with the campaigns, these groups are often staffed with a candidate's trusted friends and former top aides, who can provide crucial help even without being told what to do by anyone in the contender's camp.

Here's a look at some of the money vehicles in the 2016 presidential race:

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Direct coordination between super PAC and campaign: Hillary Rodham Clinton and Correct the Record

A group working to counter Republican criticism of the Democratic front-runner says it will listen in on Clinton campaign planning calls. Attorneys for the two entities believe they'll avoid running afoul of the Federal Election Commission because of a technicality: Correct the Record won't spend money on ads, which would trigger anti-coordination rules. Rather, it will circulate its pro-Clinton messages for free on Internet platforms such as Facebook and Twitter.

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Super PAC might outraise campaign: Jeb Bush and Right to Rise

Thanks to the super PAC that served as his campaign-in-waiting for six months, the Republican contender said he's raised more money in 100 days than any Republican operation in modern times. Bush attended dozens of fundraisers for Right to Rise, which will spend tens of millions of dollars on pro-Bush advertisements. If Right to Rise ends up with more money than the candidate's own campaign, it would be a first.

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Campaign splits to start super PAC: Ben Carson and unnamed super PAC

Houston businessman Terry Giles worked for more than a year to prepare Carson, a politically inexperienced neurosurgeon seeking the Republican presidential nomination, for his campaign launch in early May. Now Giles and others from the Carson campaign have left and plan to start a super PAC. Election rules mean that those aides must wait until September before becoming super PAC employees.

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Collection of super PACs: Ted Cruz and Keep the Promise network

Wealthy Cruz supporters opened four super PACs_Keep the Promise and Keep the Promise I through III_in the weeks after he announced his Republican presidential campaign in March. The setup ensures that donors to each will have more direct control of how their money is spent. Cruz recently said that his campaign and outside groups helping him have amassed more than $40 million.

Apart from super PACS, there are nonprofits that don't disclose their donors. It's the latest way for candidates to get an extra boost of outside assistance. While such groups must limit their direct election work, including advertising, they can promote a candidate's policies to the great benefit of a campaign. Much like Bush's Right to Rise super PAC, these nonprofits can serve as a placeholder campaign for an unannounced candidate, paying salaries of aides and travel to early primary states. That's how Louisiana Gov. Bobby Jindal is using America Next, a nonprofit policy group he created, as he weighs whether to jump into the 2016 GOP field.

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Do it yourself: If you're Donald Trump

"I'm using my own money," says the latest contender to jump in the Republican contest. "I'm not using donors." He says his net worth is $9 billion, so "I don't care. I'm really rich."